A. Field of the Invention
The present invention relates to a method and system for predicting future performance by classifying individual lamps, in one example high-intensity discharge (HID) lamps, and using the classifications in designing lighting systems using such lamps.
B. Problems in the Art
There tends to be substantial lamp-to-lamp variability in light output (typically expressed as lumens), as well as other lamp performance characteristics, between HID lamps of the same type (e.g. metal halide, high-pressure sodium, or mercury vapor of certain rated operating power in watts) and specifications (e.g. chemicals, lamp operating position, and operating parameters like operating voltage and current), including from the same lamp manufacturer. Production techniques and/or inherent properties of HID lamps produce such variances. In the example of light output, testing has found there could be on the order of 25% variation of light output from these lamps. This creates a problem when designing lighting systems for wide area lighting such as sports lighting.
Such systems utilize a plurality of HID lamps and fixtures, each with a specific location and fixture angle or aiming orientation relative to a sports field to be illuminated. The goal is to position and aim these multiple fixtures in a manner to illuminate the field in a relatively even or uniform manner with sufficient intensity for the playability of the sport. It is also a typical goal that the system be designed to be as economical as possible. For example, a usual goal is to minimize the capital costs (e.g. number and cost of lighting fixtures, lamps, poles or elevating structure, and ancillary equipment). It can also be a goal to minimize operating costs, such as energy usage (which is highly related to the number of and power consumed by the lamps).
HID lamps are typically categorized by rated operating power; as electrical energy consumed tends to correlate with light output. For example, one category of sports lighting lamp is rated at 1000 watts. Another is at 1500 watts. A 1500 watt rated lamp normally would generate more light output than a lamp of the same general characteristics but rated at 1000 watts, if both lamps are operated at or near rated power. But, as the rating implies, the 1500 watt lamp would normally consume more electrical energy per time period of operation than a 1000 watt lamp. Examples of several 1500 watt rated lamps are the Switch Start MH Std 1500 W Mog BT56 CL model commercially available from Philips Lighting Company, 200 Franklin Square Drive, Somerset, N.J. 08875 USA, and the MS 1500 W/HOR/XP/SPORT 60 model commercially available from Venture Lighting, 32000 Aurora Road, Solon, Ohio 44139 USA.
To design a lighting system, an assumption is made as to the amount of light that can be expected out of the lamps, which usually are of the same rating and from the same manufacturer. However, the large variance in actual light output, described above, presents the following serious problems for the design and installation of lighting systems of this nature.
As is known in the art, sports lighting, a type of wide-area lighting, usually must meet certain lighting criteria to meet specifications that are often imposed for a particular location or application. Organizations such as the Illuminating Engineering Society of North America (IESNA) and others have developed sports field illumination intensity and uniformity minimums for different sports that are many times used for these purposes. Many customers specify that such standards be met by the entity installing the sports lighting system.
Presently, the lighting system designer typically relies on lamp manufacturer information regarding such things as the amount of light output, its operating efficacy, its color, and its longevity when trying to design the system to meet the light intensity and uniformity specifications. However, lamp manufacturers often provide only generalized information for each lamp type. For example, a typical manufacturer may provide one or more of the following information with each type of lamp: (1) nominal or rated initial light output (RILO) (predicted lumens after 100 hours of operation); (2) nominal or initial power use (predicted lumens per watt); (3) mean light output (predicted average lumens at 40% rated life for lamp); (4) rated life of lamp (predicted median life span of large number of the type of lamp based on predicted time when 50% will fail); (5) predicted color; and (6) best lamp operating position. Some may give a general idea of predicted lamp lumen depreciation for the type of lamp (lamp lumen depreciation (LLD) is the reduction in lamp light output that progressively occurs during lamp life) (e.g. LLD curve of FIG. 1).
Take for example the generalization of LLD. It is sometimes defined to be a ratio between (a) predicted light output from the HID lamp at a specified cumulative operating time after initial start-up and (b) RILO. RILO (e.g. see FIG. 1) is usually provided by manufacturers and expresses the total light output in lumens after 100 hours of seasoning or “burn-in”. The lumen refers to a unit measurement of the rate at which a lamp produces light. As defined by IESNA publication LM-54-1991, “IES Guide to Lamp Seasoning”, lamp seasoning requires operation of an HID lamp for a considerable period of time until photometric, colorimetric, and/or electrical characteristics are constant. The publication advises this seasoning is required before any photometric, colorimetric or electrical test measurement should be collected. Seasoning for HID lamps is stated to be 100 operation hours at recommended operating parameters.
RILO is usually based on random testing of the type of lamp by the manufacturer. But since no two lamps are identical on these points, this information is a generalized estimate for all lamps of one type. As stated earlier, lamps of identical nominal operating wattage and other characteristics, make-up, or structure can vary dramatically in lumen output from each other when operated, and the magnitude of the variance can be substantial (e.g. +/−10% or more). Therefore, using the lamp manufacturer's information is not only generalized for all lamps of that particular type, but merely an educated guess for individual lamp performance for that type. Thus, when designing a system, it becomes somewhat of an educated guess as to what type, number, and RILO of lamps should be used for a given application, i.e., the use to which the lighting system will be put.
If, for example, a number of the lamps in operation produce actual light output substantially lower than assumed or manufacturer's generalized estimated light output for that type of lamp, lighting requirements for the lighting system might not be achieved when the system is installed and operated. In order to do so, the lighting system installer might have to add additional lighting fixtures after the initial installation. By lighting fixture (also referred to as a luminaire) it is meant a complete lighting unit consisting of lamp (or lamps) and the parts designed to distribute the light, position and protect the lamp(s), and connect the lamp(s) to the power supply.
The addition of lighting fixtures can be very costly to the installer and manufacturer due to extra labor, extra product cost, and potential concerns for structure loading to handle extra fixtures. Also, additional electrical equipment is needed, and the existing wiring and components may not be adequately sized for the extra electrical load of the fixtures. This can be particularly problematic if the discovery of insufficient light for the application occurs after the original lighting system is installed. As can be readily appreciated, many wide-area lighting systems must elevate the lighting fixtures to substantial heights (e.g. 30 to 150 feet). Poles or superstructure to do so are expensive and resource-intensive to install. If lamps have to be retro-fitted after initial installation, this can be quite expensive and burdensome.
Even if lighting output is just slightly low from, for example, a four pole lighting system (with three lighting fixtures per pole), the installer may have to add one fixture per pole to balance out the uniformity of light and the appearance of the fixtures on the pole. This could add on the order of 25% more fixtures. This may meet specifications, but the cost is substantial. It also may result in too much light. Many times light pollution (e.g. glare, sky glow, and spill light) must be carefully controlled. Too much light can upset the design relative to light pollution specification or restrictions. In addition, excess light from added sources or fixtures consumes extra energy, which increases operating costs. Sometimes, instead of or in addition to adding one or more extra lighting fixtures per pole, an extra light pole is needed or added to add additional fixtures, which can add significant capital cost to the lighting system.
As noted, one state of the art attempt to solve this issue is to simply add lamps and/or poles to the initial design, assuming that at least some lamps will under-perform the lamp manufacturer's estimate. But also, excess light is also a concern if the lighting system is over-designed due to better performance from the lamps than assumed in the design calculation. Having more light than needed is generally better than not enough light, but it consumes more energy than necessary to light the area per the defined specifications. Excess light may also add cost to the project due to extra fixtures and structure cost that are not needed. Thus, lamps that produce more light output than predicted by the lamp manufacturer are not used in efficient manner. Glare and spill light issues can also be created.
As indicated earlier, there might be as much as approximately + or −12% differences between low and high ends for sports lighting HID lamps. A typical range is at least +/−7%. The lighting system installer has no control over this variance. Light manufacturers are believed to do sporadic testing. Perhaps they test one to four out of 5,000 lamps. One possible reason for the low quantity of lamps tested is the cost to operate the lamps during testing and the required time of testing. HID lamps generally require a 100 hour “burn-in” or previously-described “seasoning” period to stabilize the lamp to allow for accurate measurement or estimate of light output. An HID lamp's lumen output may decrease as much as 20 percent or more in the first approximately 100 hours of use (some HID sources have other “burn-in” times; typically within a range of between approximately 50 and 200 hours). This is why lamp manufacturers will generally provide an estimate of initial lamp lumen output at the 100 hour (or other seasoning or burn-in) mark. This value is referred to in the art as “initial light output”, “rated light output”, or “rated lumen” for the lamp. It will be referred to herein as “rated initial light output” or “RILO” in lumens (“lm”) after 100 hours of seasoning.
It is simply not practical or cost effective for lamp manufacturers to test each and every lamp for actual performance. Thus, as previously stated, lamp manufacturers' lamp performance information, e.g. “100 hour burn-in” light output, rated life, mean light output, LLD, are predicted values only. An example of a typical lamp manufacturer 100 hour light output published RILO and an LLD curve estimate (if provided by lamp manufacturer) are set forth at FIG. 1. A lighting system designer can use these types of information to get a generalized, estimated prediction of lamp performance, but actual lamp performance may vary significantly.
Therefore, this is a real problem in the industry. It would be beneficial to more accurately know or predict the light output that will be put into fixtures in a lighting system.
A few specific examples illustrate some of the problems in the state of the art. As previously stated, lamp lumen output may vary by +/−7%, or more (sometimes up to on the order of +/−12%) from nominal published output or RILO for a type of lamp. This variation in output can have a positive or negative impact on the actual light output to the target area. It may cause the area to be over-lighted, or perhaps under-lighted.